Oxy-fueled aluminum recovery method

ABSTRACT

An oxygen fueled combustion system includes a furnace having at least one burner, an oxygen supply for supplying oxygen having a predetermined purity, and a carbon based fuel supply for supplying a carbon based fuel. The oxygen and the carbon based fuel are fed into the furnace in a stoichiometric proportion to one another to limit an excess of either the oxygen or the carbon based fuel to less than 5 percent over the stoichiometric proportion. The combustion of the carbon based fuel provides a flame temperature in excess of 4500° F. The exhaust gas stream from the furnace has substantially zero nitrogen-containing combustion produced gaseous compounds from the oxidizing agent and reduced green-house gases. Substantially less carbon based fuel is required than conventional combustion systems without a loss of energy output.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/843,679, filed Apr. 27, 2001, now U.S. Pat. No. 6,436,337.

BACKGROUND OF THE INVENTION

The present invention pertains to an oxygen fueled combustion system.More particularly, the present invention pertains to an oxy-fueledcombustion system in which the production of green-house gases isreduced and in which fossil fuel consumption is reduced.

Oxygen fueled burner systems are known, however, their use is quitelimited. Oxy-fueled burner systems are generally only used in thoseapplications in which extremely high flame temperatures are required.For example, these systems may be used in the glass making industry inorder to achieve the temperatures necessary to melt silica to a fusiontemperature. Otherwise, it is commonly accepted that structural andmaterial limitations dictate the upper temperatures to which manyindustrial systems can be subjected. To this end, air fueled or airfired combustion systems are used in boilers, furnaces and the likethroughout most every industrial application including manufacturing,electric power generating and other process applications.

In particular, air fueled combustion systems or electric heating systemsare used throughout the steel and aluminum making industries, as well asthe power generation industry, and other industries that rely uponcarbon based fuels. In air fueled systems, air which is comprised ofabout 79% nitrogen and 21% oxygen, is fed, along with fuel into afurnace. The air fuel mixture is ignited creating a continuous flame.The flame transfers energy in the form of heat from the fuel air mixtureinto the furnace.

In the steel and aluminum industries, air fueled furnaces and electricfurnaces have been used as the primary heat source for creating moltenmetals. With respect to air fueled furnaces, it is conventionallyaccepted that the energy requirements, balanced against the thermallimitations of the process equipment, mandate or strongly support theuse of these types of combustion systems. As to the use of electricfurnaces in the aluminum industry, again, conventional wisdom supportsthis type of energy source to achieve the temperatures necessary foraluminum processing.

One drawback to the use of air fueled combustion systems, is that thesesystems produce NOx and other green-house gases such as carbon dioxide,sulfur dioxide and the like, as an inherent result of the combustionprocess. NOx and other green-house gases are a large contributor toenvironmental pollution, including, but not limited to acid rain. Assuch, the reduction in emission of NOx and other green-house gases isdesirable, and as a result of regulatory restrictions, emission isgreatly limited. To this end, various devices must be installed on thesecombustion systems in order to limit and/or reduce the levels of NOx andother green-house gases produced.

Another drawback with respect to air fueled furnaces is that much of theenergy released from the combustion process is absorbed or used to heatthe gaseous nitrogen present in the air that is fed to the furnace. Thisenergy is essentially wasted in that the heated nitrogen gas istypically, merely exhausted from the heat source, e.g., furnace. To thisend, much of the energy costs are directed into the environment, throughan off-gas stack or the like. Other drawbacks of the air fed combustionsystems known will be recognized by skilled artisans.

Electric furnaces likewise have their drawbacks. For example, inherentin these systems as well is the need for a source of electricity that isavailable on a continuous basis, essentially without interruption. Inthat large amounts of electric power are required to operate electricfurnaces, it is typically necessary to have these electric furnaceslocated in proximity to electric generating plants and/or largeelectrical transmission services. In addition, electric furnaces requirea considerable amount of maintenance to assure that the furnaces areoperated at or near optimum efficiency. Moreover, inherent in the use ofelectric furnaces is the inefficiency of converting a fuel intoelectrical power (most large fossil fueled power stations that use steamturbines operate at efficiencies of less than about 40 percent, andgenerally less than about 30 percent). In addition, these large fossilfueled stations produce extremely large quantities of NOx and othergreen-house gases.

For example, in the aluminum processing industry, and more specificallyin the aluminum scrap recovery industry, conventional wisdom is thatflame temperatures in furnaces should be maintained between about 2500°F. and 3000° F. This range is thought to achieve a balance between theenergy necessary for providing sufficient heat for melting the scrapaluminum, and maintaining adequate metal temperatures in the molten bathat about 1450° F. Known furnaces utilize a design in which flametemperatures typically do not exceed 3000° F. to assure maintaining thestructural integrity of these furnaces. That is, it is thought thatexceeding these temperature limits can weaken the support structure ofthe furnace thus, possibly resulting in catastrophic accidents. Inaddition, stack temperatures for conventional furnaces are generallyabout 1600° F. Thus, the temperature differential between the flame andthe exhaust is only about 1400° F. This results in inefficient energyusage for the combustion process.

It is also believed that heat losses and potential damage to equipmentfrom furnaces in which flame temperatures exceed about 3000° F. faroutweigh any operating efficiency that may be achieved by higher flametemperatures. Thus, again conventional wisdom fully supports the use ofair fueled furnaces in which flame temperatures are at an upper limit ofabout 3000° F. (by flame stoichiometry) which assures furnace integrityand reduces energy losses.

Accordingly, there exists a need for a combustion system that providesthe advantages of reducing environmental pollution (attributable to NOxand other green-house gases) while at the same time providing efficientenergy use. Desirably, such a combustion system can be used in a widevariety of industrial applications, ranging from the powergenerating/utility industry to chemical processing industries, metalproduction and processing and the like. Such a combustion system can beused in metal, e.g., aluminum, processing applications in which thecombustion system provides increased energy efficiency and pollutionreduction. There also exists a need, specifically in the scrap aluminumprocessing industry for process equipment (specifically furnaces) thatare designed and configured to withstand elevated flame temperaturesassociated with such an efficient combustion system and to increaseenergy efficiency and reduce pollution production.

BRIEF SUMMARY OF THE INVENTION

An oxygen fueled combustion system includes a furnace having acontrolled environment, and includes at least one burner. The combustionsystem includes an oxygen supply for supplying oxygen having apredetermined purity and a carbon based fuel supply for supplying acarbon based fuel. The present oxy fuel combustion system increases theefficiency of fuel consumed (i.e., requires less fuel), produces zeroNOx (other than from fuel-borne sources) and significantly less othergreen-house gases.

The oxygen and the carbon based fuel are fed into the furnace in astoichiometric proportion to one another to limit an excess of eitherthe oxygen or the carbon based fuel to less than 5 percent over thestoichiometric proportion. The combustion of the carbon based fuelprovides a flame temperature in excess of about 4500° F., and an exhaustgas stream from the furnace having a temperature of not more than about1100° F.

The combustion system preferably includes a control system forcontrolling the supply of carbon based fuel and for controlling thesupply of oxygen to the furnace. In the control system, the supply offuel follows the supply of oxygen to the furnace. The supply of oxygenand fuel is controlled by the predetermined molten aluminum temperature.In this arrangement, a sensor senses the temperature of the moltenaluminum.

The carbon based fuel can be any type of fuel. In one embodiment, thefuel is a gas, such as natural gas, methane and the like. Alternately,the fuel is a solid fuel, such as coal or coal dust. Alternately still,the fuel is a liquid fuel, such a fuel oil, including waste oils.

In one exemplary use, the combustion system is used in a scrap aluminumrecovery system for recovering aluminum from scrap. Such a systemincludes a furnace for containing molten aluminum at a predeterminedtemperature, that has at least one burner. The recovery system includesan oxygen supply for supplying oxygen to the furnace through thecombustion system. To achieve maximum efficiency, the oxygen supply hasan oxygen purity of at least about 85 percent.

A carbon based fuel supply supplies a carbon based fuel. The oxygen andthe carbon based fuel are fed into the furnace in a stoichiometricproportion to one another to limit an excess of either the oxygen or thecarbon based fuel to less than 5 percent over the stoichiometricproportion. The combustion of the carbon based fuel provides a flametemperature in excess of about 4500° F., and an exhaust gas stream fromthe furnace having a temperature of not more than about 1100° F.

In such a recovery system, the combustion of oxygen and fuel createsenergy that is used for recovering aluminum from the scrap at a rate ofabout 1083 BTU per pound of aluminum recovered. The fuel can be a gas,such as natural gas, or it can be a solid fuel or a liquid fuel.

In the recovery system, heat from the furnace can be recovered in awaste heat recovery system. The recovered heat can be converted toelectrical energy.

In a most preferred system, the combustion system includes a system forproviding oxygen. One such system separates air into oxygen andnitrogen, such as a cryogenic separation system. Other systems includemembrane separation and the like. Oxygen can also be provided by theseparation of water into oxygen and hydrogen. In such systems, theoxygen can be stored for use as needed. Other systems are known foroxygen generation/separation.

The oxygen fueled combustion system, generally, can be used with anyfurnace that has a controlled environment. That is, with any furnacethat has substantially no in-leakage from an external environment. Sucha combustion system includes an oxygen supply for supplying oxygenhaving a predetermined purity and a carbon based fuel supply forsupplying a carbon based fuel.

The oxygen in the oxygen supply and the carbon based fuel are fed intothe furnace in a stoichiometric proportion to one another to limit anexcess of either the oxygen or the carbon based fuel to less than 5percent over the stoichiometric proportion. In such a furnace, anexhaust gas stream from the furnace has substantially zeronitrogen-containing combustion produced gaseous compounds. That is,because there is no nitrogen fed in with the fuel, unless there isfuel-borne nitrogen, the exhaust gas contains substantially no nitrogencontaining combustion products (i.e., NOx), and significantly loweredlevels of other green-house gases.

This combustion system can use any carbon based fuel including gas, suchas natural gas or methane, any solid fuel such as coal or coal dust orany liquid fuel, such as oil, including waste and refined oils. In sucha combustion system, any nitrogen-containing combustion produced gaseouscompounds are formed from the fuel-borne nitrogen.

A method for recovering aluminum from scrap includes feeding aluminumscrap into a melting furnace and combusting oxygen and a carbon basedfuel in the furnace. In the combustion of the oxygen and fuel, theoxygen and fuel are fed into the furnace in a stoichiometric proportionto one another to limit an excess of either the oxygen or the carbonbased fuel to less than 5 percent over the stoichiometric proportion.The combustion provides a flame temperature in excess of about 4500° F.,and an exhaust gas stream from the furnace having a temperature of notmore than about 1100° F.

The aluminum is melted in the furnace, contaminant laden aluminum isremoved from the furnace and substantially pure molten aluminum isdischarged from the furnace. The method can include the step ofrecovering aluminum from the contaminant laden aluminum, i.e., dross,and charging the recovered aluminum into the furnace.

The method can include recovering waste heat from the furnace. The wasteheat recovered can be converted to electricity.

A furnace for recovering aluminum from scrap aluminum includes a bathregion for containing molten aluminum at a predetermined temperature,and at least one burner. An oxygen supply supplies oxygen having apurity of at least about 85 percent and a carbon based fuel supplysupplies fuel, such as natural gas, coal, oil and the like.

The oxygen in the oxygen supply and the fuel are fed into the furnace ina stoichiometric proportion to one another to limit an excess of eitherthe oxygen or the fuel to less than 5 percent over the stoichiometricproportion. The combustion of the fuel provides a flame temperature inexcess of about 4500° F., and an exhaust gas stream from the furnace hasa temperature of not more than about 1100° F.

In one embodiment, the furnace is formed from steel plate, steel beamsand refractory materials. The furnace walls are configured having asteel beam and plate shell, at least one layer of a crushable insulatingmaterial, at least one layer of a refractory brick, and at least onelayer of a castable refractory material. The furnace floor is configuredhaving a steel beam and plate shell and at least two layers ofrefractory material, at least one of the layers being a castablerefractory material.

A salt-less method for separating aluminum from dross-laden aluminum isalso disclosed that includes the steps of introducing the dross-ladenaluminum into a furnace. The furnace has an oxygen fuel combustionsystem producing a flame temperature of about 5000° F., and havingsubstantially no excess oxygen. The dross-laden aluminum melts withinthe furnace.

An upper portion of the melted dross-laden aluminum is skimmed toproduce a heavily dross-laden product. The heavily dross-laden productis pressed in a mechanical press to separate the aluminum from theheavily dross-laden product to produce a concentrated heavilydross-laden product. The method can include the step of returning theconcentrated heavily dross-laden product to the furnace. Introduction ofthe dross-laden aluminum into the furnace is carried out in near directflame impingement to release the oxides from the dross.

These and other features and advantages of the present invention will beapparent from the following detailed description, in conjunction withthe appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The benefits and advantages of the present invention will become morereadily apparent to those of ordinary skill in the relevant art afterreviewing the following detailed description and accompanying drawings,wherein:

FIG. 1 is an overall flow scheme of an exemplary aluminum scrap recoveryprocess having a melting furnace with an oxygen fueled combustionsystem, in which green-house gas production and fuel consumption arereduced, embodying the principles of the present invention;

FIG. 2 is an overall flow scheme of a dross processing operationcontinued from FIG. 1 having a recovery furnace having an oxygen fueledcombustion system embodying the principles of the present invention;

FIG. 3 is an exemplary natural gas supply train and oxygen supply trainfor use with the oxygen fueled combustion system;

FIG. 4 is an overall plant scheme showing the oxygen supply, from acryogenic plant, and flow to the furnaces, and further illustrating anexemplary waste heat recovery plant;

FIG. 5 is a schematic illustration of an aluminum melting furnace foruse with an oxygen fueled combustion system in accordance with theprinciples of the present invention;

FIG. 6 is a side view of the furnace of FIG. 5;

FIG. 7 is a front view of the melting furnace of FIG. 6;

FIGS. 8 and 9 are partial cross-sectional illustrations of a side walland the floor of the furnace, respectively;

FIG. 10 illustrates a burner assembly for use with the oxygen fueledcombustion system;

FIG. 11 is a schematic illustrations of an exemplary control system foruse with an oxygen fueled combustion system of the present invention

FIG. 12 is a schematic view of an exemplary power boiler or furnacefront wall illustrating a burner and an air feed arrangement, andshowing the incorporation of an oxy fuel combustion system thereinembodying the principles of the present invention; and

FIG. 13 is a schematic illustration of a waste incinerator showing theincorporation therein of an oxy fuel combustion system embodying theprinciples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is susceptible of embodiment in variousforms, there is shown in the drawings and will hereinafter be describeda presently preferred embodiment with the understanding that the presentdisclosure is to be considered an exemplification of the invention andis not intended to limit the invention to the specific embodimentillustrated. It should be further understood that the title of thissection of this specification, namely, “Detailed Description Of TheInvention”, relates to a requirement of the United States Patent Office,and does not imply, nor should be inferred to limit the subject matterdisclosed herein.

An oxy-fuel combustion system uses essentially pure oxygen, incombination with a fuel source to produce heat, by flame production(i.e., combustion), in an efficient, environmentally non-adverse manner.Oxygen, which is supplied by an oxidizing agent, in concentrations ofabout 85 percent to about 99+ percent can be used, however, it ispreferable to have oxygen concentration (i.e., oxygen supply purity) ashigh as possible. In such a system, high-purity oxygen is fed, alongwith the fuel source in stoichiometric proportions, into a burner in afurnace. The oxygen and fuel is ignited to release the energy stored inthe fuel. For purposes of the present disclosure, reference to furnaceis to be broadly interpreted to include any industrial or commercialheat generator that combusts fossil (carbon-based) fuels. In a preferredsystem, oxygen concentration or purity is as high as practicable toreduce green-house gas production.

It is contemplated that essentially any fuel source can be used. Forexample, in a present application, as will be described in more detailbelow, oxygen is fed along with natural gas, for combustion in afurnace. Other fuel sources contemplated include oils including refinedas well as waste oils, wood, coal, coal dust, refuse (garbage waste) andthe like. Those skilled in the art will recognize the myriad fuelsources that can be used with the present oxy-fuel system.

The present system departs from conventional processes in two principalareas. First, conventional combustion processes use air (as an oxidizingagent to supply oxygen), rather than essentially pure oxygen, forcombustion. The oxygen component of air (about 21 percent) is used incombustion, while the remaining components (essentially nitrogen) areheated in and exhausted from the furnace. Second, the present processuses oxygen in a stoichiometric proportion to the fuel. That is, onlyenough oxygen is fed in proportion to the fuel to assure completecombustion of the fuel. Thus, no “excess” oxygen is fed into thecombustion system.

Many advantages and benefits are achieved using the present combustionsystem. It has been observed, as will be described below, that fuelconsumption, to produce an equivalent amount of power or heat isreduced, in certain applications, by as much as 70 percent.Significantly, this can provide for a tremendous reduction in the amountof pollution that results. Again, in certain applications, the emissionof NOx can be reduced to essentially zero, and the emission of othergreen-house gases reduced by as much as about 70 percent overconventional air-fueled combustion systems.

An Exemplary Scrap Aluminum Recovery Process

In one specific use, the oxygen fueled combustion system (also referredto as oxy-fuel or oxy-fueled) is used in a scrap aluminum recovery plant10. A flow process for an exemplary plant is illustrated in FIGS. 1-2.Scrap aluminum, generally indicated at 12 is fed into a melting furnace14, and is liquefied. The plant 10 can include multiple furnacesoperated in parallel 14, one of which is illustrated. The liquefied ormolten aluminum is drawn from the melting furnace 14 and is fed into asmaller holding furnace or holder 16. The holding furnace 16 is also anoxy-fueled furnace. The molten aluminum is drawn from the meltingfurnace 14 as necessary, to maintain a certain, predetermined level inthe holding furnace 16. This can result in continuously drawing downfrom the melting furnace 14 or drawing down in “batches” as required.

In the holding furnace 16, chlorine and nitrogen (as gas), as indicatedat 18 and 20, respectively, are fed into the holding furnace 16 tofacilitate drawing the impurities from the molten aluminum. The chlorineand nitrogen function as a gaseous fluxing agent to draw the impuritiesfrom the aluminum. This can also be carried out in the melting furnaces14 to increase cleaning of oily and dirty scrap. Other contemplatedfluxing agents include gaseous argon hexafluoride. The holder 16 isactively heated and operates at a molten metal temperature of about1300° F. The air temperature in the holder 16 is slightly higher.

The molten aluminum is then filtered. Presently, a bag-type particulatefilter 22 is used. However, other types of filters are known and can beused. The filtered, molten aluminum is then fed through a degasser 24.

In the degasser 24, a fluxing agent, such as an inert gas (again,nitrogen is used, as indicated at 26) is fed into the molten aluminum.The molten aluminum is agitated, such as by a mechanical stirrer 28 andthe fluxing agent 26 bubbles up through the molten aluminum to drawimpurities (e.g., oxides) from the aluminum.

The molten aluminum is then fed into an in-line caster 30. In the caster30, the aluminum is cast into continuous plate. The cast thickness canbe any where from 0.010 inches up to 0.750 inches or more. The aluminumcan then be rolled into a coil, as indicated at 32, for use or furtherprocessing. In a present method, the aluminum proceeds from the caster30 through a pair of hot milling machines 34 where the plate is milledto a final thickness or gauge, presently about 0.082 inches (82 mils)and is then rolled to form the coil 32. Those skilled in the art willunderstand and appreciate the various end forming and finishingprocesses that can be carried out on the metal. All such forming andfinishing processes are within the scope and spirit of the presentinvention.

Returning to the melting furnace 14, as stated above, it is an oxy-fuelfurnace. It is fed with a carbon based fuel, such as natural gas, instoichiometric proportion with oxygen. This is unlike known furnaceswhich use fuel and air mixtures. The fuel/air mixtures feed nitrogen aswell as oxygen into the furnace to support the combustion process. Thisresults in the production of undesirable NOx off-gases. In addition, thenitrogen also absorbs energy from the molten aluminum, thus reducing theoverall efficiency of the process. That is, because the percentage ofnitrogen in air is so great, a large amount of energy goes into heatingthe nitrogen rather than the aluminum.

The oxygen/natural gas proportions in the present melting and holdingfurnaces 14, 16 are about 2.36:1. This ratio will vary depending uponthe purity of the oxygen supply and the nature of the fuel. For example,under perfect conditions of 100 percent pure oxygen, the ratio istheoretically calculated to be 2.056:1. However, the oxygen supply canhave up to about 15 percent non-oxygen constituents and natural gas isnot always 100 percent pure. As such, those skilled in the art willappreciate and understand that the ratios may vary slightly, but thebasis for calculating the ratios, that is stoichiometric proportions offuel and oxygen, remains true.

This proportion of oxygen to fuel provides a number of advantages.First, this stoichiometry provides complete combustion of the fuel, thusresulting in less carbon monoxide, NOx and other noxious off-gasemissions (other green-house gases generally). In addition, thecontrolled oxygen proportions also reduce the amount of oxides presentin the molten aluminum. This, in turn, provides a higher quality finalaluminum product, and less processing to remove these undesirable oxidecontaminants.

It is important to note that accurately controlling the ratio of oxygento fuel assures complete burn of the fuel. This is in stark contrast to,for example, fossil fueled power plants (e.g., utility power plants),that struggle with LOI (loss on ignition). Essentially, LOI equates toan incomplete burn of the fuel. In the present method, on the otherhand, substantially pure oxygen, in tightly controlled stoichiometricproportion to the fuel, minimizes and possibly eliminates these losses.In addition, in the present method, the only theoretical NOx availableis from fuel-borne NOx, rather than that which could otherwise resultfrom combustion using air. Thus, NOx, if not completely eliminated isreduced to an insignificant amount compared to conventional combustionsystems.

Oxides in aluminum come from two major sources. First, from thecombustion process; second, from oxides that reside in the aluminum.This is particularly so with poor grade scrap or primary metal. Thepresent process takes into consideration both of these sources of oxidesand reduces or eliminates their impact on the final aluminum product.First, the present process reduces oxides that could form as a result ofthe oxygen fed for the combustion of the fuel. This is achieved bytightly controlling oxygen feed to only that necessary by stoichiometricproportion for complete combustion of the fuel.

The present process takes into consideration the second sources ofoxides (that residing in the aluminum), and removes these oxides byvirtue of the degassing and filtering processes. The benefits are twofold. The first is that less byproduct in the form of dross D is formed;second, the quality of the finished product is greatly enhanced.

It has also been found that using a fuel/oxygen mixture (again, ratherthan a fuel/air mixture) results in higher flame temperatures in themelting furnace. Using oxy-fuel, flame temperatures in the furnace ofabout 5000° F. are achieved. This is higher, by about 1500° F. to 2000°F., than other, known furnaces. It has also been observed that usingoxy-fuel, in conjunction with these higher flame temperatures, resultsin an extremely highly efficient process. In one measure of efficiency,the energy required (in BTU) per pound of processed aluminum ismeasured. In a known process, the energy required is about 3620 BTU/lbof processed product. In the present process and apparatus, the energyrequirements are considerably less, about 1083 BTU/lb of metalprocessed. It should also be noted that although the “fuel” discussedabove in reference to the present method is natural gas, any organicbased fuel, such as oil (including waste oil), coal, coal dust and thelike can be used.

For purposes of understanding the thermodynamics of the process, thetheoretical energy required to melt a pound of aluminum is 504 BTUs.However, because specific process inefficiencies are inherent, theactual energy required was found to be about 3620 BTU/lb when using anair fired combustion system. These inefficiencies include, for example,actual processing periods being less than the actual time that thefurnace is “fired”, and other downstream process changes, such as casterwidth increases or decreases. In addition, other “losses” such as stack(heat) losses, and heat losses through the furnace walls, add to thisenergy difference.

Moreover, the value of 1083 BTU/lb is an average energy requirement,even taking into account these “losses”. It has been found that when theprocess is running at a high efficiency rate, that is when aluminum isprocessed almost continuously, rather than keeping the furnace “fired”without processing, the “average” energy requirement can be reduced toabout 750BTU/lb to 900BTU/lb.

The Melting Furnace

A present melting furnace 14 is constructed primarily of steel andrefractory materials. Referring to FIGS. 5-9, the furnace shell 42 hasoutside dimensions of about 20 feet in width by 40 feet in length by 12feet in height. The steel shell structure 42 is formed from plates andbeams. Plates and beams will be identified through as 44 and 46,respectively, for the furnace shell 42 structure, except as indicated.The floor 48 is fabricated from one-inch thick plate 44 steel that iswelded together. Each weld is above a beam 46 to assure the integrity ofthe furnace shell 42.

Additional beams 46 are provided for furnace floor 48 support. Each beam46 provides an 8 inch wide flange about every 18 inches on center. Allof the beams 46 (exclusive of the joining beams which are completelyseam welded) are stitched to the bottom plate 50. This permits “growth”in the steel due to thermal expansion during heating.

The beams 46 provide support and rigidity to the furnace bottom 52. Thebeams 46 maintain the furnace 14 rigid to reduce flexing duringinstallation of the refractory and long-term use. The beams 46 alsoprovide support so that during operation of the furnace 14 themechanical loading on the refractory materials is minimized. The beams46 also elevate the furnace bottom 52 from the floor on which thefurnace 14 is mounted. This allows heat, which builds up under thefurnace 14, to escape.

The furnace side walls 54 are likewise made of a steel plate and beamconstruction. Two wall regions are recognized, above metal line andbelow metal line. This distinction is made for both strength and thermalvalue considerations.

Below metal line, the plate is ¾ inch thick. Above metal line, the plateis ⅝ inch thick. In the present furnace, the first eight feet areconsidered (for design purposes) below metal line and the upper fourfeet are considered (for design purposes) above metal line.

Beams 46 are used to support the side walls 54 of the furnace 14. Thebeams 46 are set on 18 inch centerlines running vertically along thefurnace 14. Horizontal beams 46 are placed at 18 inch centers belowmetal line and 24 inch centers above metal line. Although the metal linein the furnace 14 varies, it is, for design considerations, the highestlevel of metal that will be in the furnace 14 during normal operation.Additional factors may be considered, in which, for example, the metalline can be assumed to be nine inches above the maximum fill line of thefurnace 14.

The roof 56 of the furnace 14 is a hanging refractory design. Beams 46are on 18 inch centers along the width of the furnace 14. Additionalbeams 46 are welded to beams extending across the width, whichadditional beams are oriented along the length of the furnace 14. Clipsare mounted to the beams, to which precast refractory blocks aremounted.

The furnace 14 has two main doors 58 on the furnace side 54. The doors58 are used during operation for skimming or cleaning the main furnaceheat chamber or bath area 60 and for main furnace chamber 60 charging.Dross D (the contaminant slag that forms of the surface of moltenaluminum) builds up inside the furnace 14 and must be cleaned out atleast once a day to maintain heat transfer rates. The dross D is removedby opening the doors 58 and skimming the surface of the molten metalpool.

Although during typical operation, metal or scrap is placed in thecharge well 62, and is subsequently melted and transferred to thefurnace heat chamber 60, some types of scrap, such as sows or ingot, arebetter placed directly in the main heat chamber 60. The doors 58 can beopened to transfer these types of loads to the heat chamber 60.

The doors 60 are of steel and refractory construction. The doors 60 arehung on a mechanical pulley system (not shown) and are protected bysafety chains to prevent them from falling to the ground in the eventthat the pulley system fails. Powered winches are used to operate thedoors. The doors 60 are hung from a common cross member, which issupported from the side 54 of the furnace 14.

The main charge well 62 is located on the front 64 of the furnace 14.The well 62 is partitioned from the furnace heat chamber 60 and ispartitioned into two areas: a charging area 66; and a circulation pumparea 68. A circulation pump 70 circulates metal from the hot pool ofmolten aluminum in the main chamber 60 to the scrap charging area 62.

There are three openings, indicated at 72, 74 and 76, between thechambers 60, 66 and 68. The first opening 72 is in the partition betweenthe main chamber 60 and the pump well 68. The second opening 74 is inthe partition between the pump well 68 and the scrap charging area 66.The third opening 76 is in the partition between the charge well 66 andthe main heat chamber 60.

All of the openings 72, 74 and 76 are about one foot below the physicalor actual metal line of the furnace 14. The openings 72, 74 and 76 arebelow metal line to maintain the heat inside the main chamber 60, and toprevent the flow of oxides between the partitioned areas of the furnace14 and to maintain the furnace air-tight (i.e., maintain a controlledenvironment within the furnace 14). The pump 70 is located in anelevated area to prevent excessive furnace garbage, rocks and dross fromaccumulating in and around the pump 70.

An exhaust hood 78 is positioned above the charge chamber 66. The hood78 is fabricated from steel and is mounted on beams 46 similar to thosefrom which the side walls 54 are fabricated. The beams 46 are positionedon a plate that covers the side wall of the well, essentially capping itoff. The hood 78 vents the main furnace chamber 60 through a stack 80(see FIG. 4). The stack 80 exhausts gases from the furnace 14 and can beclosed off to maintain pressure in the furnace 14.

Exhaust gases exit the furnace 14 and flow to a baghouse 82 (FIG. 4).The baghouse 82 is used primarily for collection of unburned carbon frompaints, oils, solvents and the like inherent in scrap aluminumprocessing.

The furnace 14 includes four oxy-fuel burners 84. The burners 84 areinstalled on a side wall 54 of the furnace 14, opposite the doors 58.Steel is constructed surrounding the burners 84 to allow for mountingthe burners 84 and maintaining the surrounding wall rigid.

The furnace 14 is lined with refractory materials. The floor 48 isfabricated from two different refractory materials. The first material86 is a poured slab, about six inches thick, of a high strength,castable refractory, such as AP Green KS-4, that forms a sub hearth. Afloor material 88 is poured above the sub hearth 86 in monolithicfashion having a thickness of about thirteen to fourteen inches. Thefloor material 88 is an AP Green 70AR refractory. It is a 70 percentalumina, aluminum resistant castable refractory.

The walls 54, 64 and 65 are fabricated from two layers of insulation 90followed by the 70 AR castable or monolithic, phosphate bonded 85percent alumina (MONO P85) plastic ramming refractory 92. The aluminacontent of this material is 85 percent. The backing insulation 90 isinsulating board, about two inches thick in the side walls 54 of thefurnace and about three inches thick on the front and rear walls 64, 65of the furnace. The difference in insulation 90 thickness is toaccommodate thermal expansion of the furnace 14. The furnace walls 54,64 and 65 will grow about ⅛ inch per linear foot. Thus, the furnace 14will grow (along the 40 foot length) a total of about 5 inches. In thatthere is six inches of backing insulation 90 (each the front and rearhas three inches), the insulation 90 will crush and allow for growth inthe furnace walls 54, 64 and 65 without damaging the furnace shell 42.

Insulating brick 94 is positioned between the crushable insulation board90 and the cast refractory 92. The roof 56 is fabricated from 70 percentalumina castable refractory. The material is poured into six roofsections. Each door 58 frame is fabricated from 70 percent alumina ARrefractory.

The furnace 14 has two sets of tap out blocks (not shown). The first setis positioned on the bottom 52 of the furnace and serve as drain blocks.A second set of blocks is positioned sixteen inches from the floor ofthe furnace and serves as a transfer set of blocks. The transfer blocksare set on the outside of the furnace for ease of replacement. Theinside of the furnace is formed and the blocks are set on the outsideand keyed in with a plastic ram.

There are two ramps (not shown) in the furnace, one at each of the maincharge doors 58. The ramps are used for deslagging or skimming dross Dfrom the molten metal and for allowing scrap aluminum to slide into thefurnace. The ramps are composed of two materials. The base is a lowgrade aluminum resistant brick, stacked to form a ramp. The brick iscovered with a castable refractory (about 18 inches thick), such as the70AR material. The ramp extends from the edge of the sill into thefurnace.

The wall 96 that separates the main furnace chamber 60 and the chargewell 62 is about 22 inches thick and is formed from 70AR material. Thewall 96 is cast as a single monolithic structure.

The furnace 14 can operate in several modes from empty to holding andmaintaining molten aluminum. When the furnace 14 is at peak operation itis about 80 percent to 90 percent full. The molten metal is at about1400° F. and the air temperature in the furnace is about 1800° F. Thestack (exhaust) temperature is about 1000° F. Air temperature ismeasured by a thermocouple 98 in the upper side wall 54 of the furnace14. Metal temperature is measured at the base of the circulating pump70.

Scrap is charged or introduced to the furnace in the charge well 62 inincrements of about 3,000 pounds. It will be understood that the size orweight of the introduced scrap will vary depending upon the size andcapacity of the furnace 14.

Molten metal from the main chamber 60 is pumped onto the cool metalcharge by the circulation pump 70. The molten metal transfers heat, byconductivity, to the cold metal charge. The charge metal rapidly heatsand melts.

The primary mode of heat transfer to the charged aluminum is byconduction. The large heat sink provided by the full furnace enhancesthis effective method of heat transfer. When the furnace is 80 percentto 90 percent of capacity there is about 220,000 pounds of moltenaluminum at about 1400° F. When scrap is charged into the furnace 14 thebath acts as a heat sink and provides the necessary energy for heattransfer to the charged metal. This is true regardless of the dimensionsand capacity of the furnace, as adapted to the present oxy-fuelcombustion system. The circulating pump 70 assists melt of the scrap byproviding hot molten metal to the charge well 62 from the main furnacechamber 60. In addition, by circulating the molten metal, heatstratification throughout the furnace 14 is maintained low.

It has been found that by pumping or circulating the molten metal, thetemperature differential between the top and the bottom of the furnace14 (a height difference of about 42 inches) is only a few degreesFahrenheit. Thus, the furnace 14 acts as a stable heat sink to provide aconsistent heat source for conduction heat transfer to the charge metal.

Heat is input to the furnace 14 by the burners 84. It is believed thatthe principal mode of heat transfer to the furnace 14 is radiation, withsome convective heat transfer. Because of the high flame temperatures,the oxy fuel combustion system provides efficient radiative heattransfer. The geometry of the furnace 14 is further designed to increasethe heat transfer rate by maximizing the metal surface area over whichheat transfer from the flame to the metal occurs.

In addition, the refractory materials above the metal line are made of ahigh alumina content material. These materials reflect the heat from theburners back into the molten metal. This is in contrast to conventionalfurnace designs which, rather than reflecting heat back into the moltenmetal pool, permit much of the heat to escape from the furnace.

For example, traditional furnaces use refractories that have a loweralumina content and a higher insulation value on the upper side walls.The present design, on the other hand, uses higher alumina contentrefractories in order to reflect more of the radiative heat from theburners 84 to the bath area 60. Again, this is contrary to conventionalfurnace design. In traditional furnaces the lower side walls (defined asbelow metal line) use higher alumina refractories for strength. Incontrast, the present design uses a lower alumina castable refractory,which is more advanced and has a higher insulating value. In a sense thepresent design goes completely against the traditional application ofrefractories.

Moreover, because there is no nitrogen fed to the furnace 14 (other thanfuel-borne nitrogen) the volume of hot gases (e.g., exhaust) goingthrough the furnace 14 is very low. Advantageously, this increases theresidence time of the gases in the furnace 14 providing additionalopportunity for heat transfer to the molten metal. Convective heattransfer, while relatively low, is more efficient than in conventionalfurnaces. In that the hot gases in the present furnace 14 approach 5000°F. and have a relatively long residence time, much of the heat isremoved prior to exhaust.

A present furnace 14 operates at an energy input required to melt ofabout 1083 BTU per pound. The maximum heat input to the furnace 14 isabout 40 million BTU (40 MMBTU) per hour, and typical heat input isabout 10 to 12 MMBTU per hour. The heat input will, of course, dependupon the scrap being melted and the production requirements. The furnaceis capable of melting up to 40,000 pounds per hour.

The Combustion System

The combustion system, indicated in FIG. 3, generally at 100, is a dualcombustion train that operates on a fuel, such as natural gas, fuel oil,waste oil, coal (pulverized, dust and liquefied), and an oxygen source.The system is designed as two complete combustion systems to facilitatemaintenance, as well as to conserve energy during low use periods. Oneoxygen train 102 and one exemplary natural gas fuel train 104 are shownin FIG. 3.

The combustion system 100 is controlled by a control system (illustratedin FIG. 11, indicated generally at 120) that includes a centralprocessing unit (“CPU”) 106 that monitors all data inputs from metaltemperature, air temperature, fuel and oxygen flow, and provides anoperator interface. Each combustion train can be operated individuallyor in tandem based on operating conditions and requirements.

The main process input variable used to control the combustion system100 is the metal bath temperature as measured by a thermocouple 108.Alternative process input variables include signals from one of severalair temperature sensors 98, 110. The control scheme includes inputs fromthermocouples (type K) located in the furnace upper wall, exhaust stackand furnace roof, indicated generally as inputs 112. The primarythermocouple 108 is located in the molten metal bath are 60. The airthermocouples 112 are sheathed with alumina or like materials to protectthe measuring element from the atmosphere. The bath thermocouple 108 isprotected from molten metal by a ceramic sheath that is resistant toheat and to the corrosive conditions found in molten metal. The baththermocouple 108 is configured to signal initiation of the burner systemonly when the metal bath temperature falls below a preset level.

The stack thermocouple or the roof thermocouple 116 is designed for overtemperature protection. This thermocouple 116 is connected to anover-temperature circuit that shuts down the combustion trains 102, 104to protect the refractory and furnace 14 structure in the event that anover temperature limit is reached.

The upper wall thermocouple 98 is primarily used to monitor the furnace14 air temperature. It can also be used to operate the furnace 14 in theabsence of the molten bath thermocouple 108. The upper wall thermocouple112 is also used as the process input variable when metal is first beingcharged in the furnace 14 or when the level of molten metal drops belowthe molten bath thermocouple 108.

An operator has full control over individual temperature set points. Acontrol panel 118 includes temperature indicators for all of thethermocouples 92, 108, 110, 112, 114, 116. The operator can adjust eachthermocouple set point until operation limits are achieved. Theoperational set point limits can be internally set within the CPU sothat any desired temperature range can be established.

The combustion system control system 120 is configured in two parts. Thefirst part 122 includes hard wired safety devices, such as relays, limitswitches and the like, as will be recognized by those skilled in theart. These include all gas pressure switches, shut off and blockingvalves, and flame detectors. The second part 124 of the control system120 is monitoring and automatic control functions carried out by the CPU106.

The gas trains 104 are configured in pairs so that one train can be inservice while the other is out of service for, for example, maintenanceor low-load/use periods. Each gas train 104 is appropriately sizedvis-à-vis oxygen flow requirements. Each gas train 104 commences at aball-type shut off valve 130. Piping 132 routes the gas through astrainer 134 to remove any debris present in the line. A gas pilot line136 extends from the piping 132 after the strainer 134.

A backpressure regulator 138 is used to lower the header pressure.Presently, the oxygen pressure is set at about 18 pounds per square inch(psig). A shut off valve 140 and safety valves 142 follow in line. Adifferential pressure flow meter 144 is located downstream of the safetyvalves 142. The flow meter 144 measures the temperature and differentialpressure of the gas as it flows through an orifice 146. A present flowmeter 144 is a Rosemount model 3095 differential pressure flow meter.

Through these measurements a flow rate is determined and a signal istransmitted to the control system 120. A control valve 148 is in linefollowing the flow meter 144. In a present arrangement, a modulatingcontrol valve is used that receives an output signal from the controlsystem 120. The valve 148 transmits a signal to the control system 120,and specifically, the CPU 106, indicating the actual valve 148 position.

The gas train 104 then splits into two separate lines 104 a,b eachhaving a valve 150 a,b. The valves 150 a,b are used to balance eachburner 84 so that the gas flow is evenly distributed.

The oxygen train 102 is similar to the gas train 104, except that theline sizes and components are larger to accommodate the larger flow rateof oxygen. An exemplary oxygen train 102 is illustrated in FIG. 3, inwhich those components corresponding to fuel train 104 components areindicated by 200 series number identifiers.

Referring to FIG. 10, the burners 84 are a fairly straight forwarddesign. Each of the four burners 84 includes a main inlet nozzle body152 that extends into the furnace 14. A fuel gas inlet 154 extends tothe main inlet body 152 external of the furnace wall 54. Oxygen is inputto the main inlet nozzle body 152 and mixes with the fuel gas. Anigniter (not shown) extends through a central opening 156 in the maininlet body 152. The igniter provides a spark for ignition of thefuel/oxygen mixture.

Operation of the combustion system 100 is readily carried out by acombination of operated initiated action and automatic control by theCPU 106. Power is provided to the system controls which enables the CPU106 and the hard-wired safeties portion 122 of the control system 120.The CPU 106 initiates communication with the control valves,thermocouples, and relays that are part of the hard-wired safetiesportion 122. The gas and oxygen pressure switches are of a dual hi/lowswitch design. The low-pressure switch is a normally closed signal whilethe high-pressure side is a normally open signal. The CPU 106 determineswhether a the proper signal is present and allows the program tocontinue. If an improper signal is recognized, audible and visual alarmsare actuated. The control scheme also monitors whether the gas andoxygen control valves 148, 248 are in the “low-fire” position. If thecontrol valves 148, 248 are in the proper position, a signal istransmitted that allows the control system 120 to continue the startupprocedure. An over-temperature signal must also be clear to allow thesystem 120 to continue through the start up procedure.

When all of the startup conditions are met, a nitrogen purge cycle isinitiated. Nitrogen is used to purge the furnace 14 of any combustiblegases that may be remaining in the furnace 14. The nitrogen purge istimed so that the volume of nitrogen through the furnace 14 is about 2.5times the volume of the furnace 14.

After the purge is complete, one or both of the combustion trains isstarted. A control switch places either a pair of burners or all of theburners 84 into operation. A flame controller opens the pilot solenoids.The pilot solenoids are normally closed, however, upon starting, thesolenoids are opened and gas and oxygen flow through a pilot assembly.

At the tip of the pilot assembly the gases mix and are ignited by aspark emitted controlled by the flame controller. Upon ignition, a flamedetector 126 detects the presence or absence of flame and transmits asignal to the control system 120. Once a flame is detected, the controlsystem 120 opens the main blocking valves for both the gas and oxygen.

The main fuel and oxygen shut off valves 140, 240 operate independently.The safety valves 142, 242 are configured such that if the gas valve 140does not open, the safety valves 142, 242 do not open. When the main gasvalve 140 opens, the gas and oxygen safety valves open 142, 242. Withall of the main valves open, a control relay is energized as well as anindicator light for each gas train on the control panel 118. A pilottimer remains energized for a preset time period, about 30 seconds. Oncethe preset time duration has elapsed, the pilot circuit is de-energizedand the normally closed solenoid valves are de-energized, isolating thepilot assemblies and the pilot indicator light for each burner train.

The flame detectors 126 continuously monitor the flame. Upon loss offlame indication, an alarm signal is transmitted to the CPU 106 and thecontrol circuit isolates the gas and oxygen shut off valves 140, 240 andblocking valves 142, 242.

Once the pilots are de-energized, furnace automatic operation is assumedby the control system 120. While the system 120 is set to “low fire”,the oxygen control valves 248 are maintained in the closed positionregardless of process and set point values. The gas control valves 148are not limited in their range since gas flow follows oxygen flow. Thecontrol system 120 maintains the gas at the preset ratio.

When operating in the automatic mode, the control system 120 responds todeviations from the process and set point values. Furnace temperature ismonitored and matched to the temperature set point. When the processtemperature deviates from the set point temperature, an error signal isgenerated, and the control system 120 transmits a signal to the oxygencontrol valve 248. The gas control valve 148 is also controlled by thecontrol system 120; the set point variable follows the(stoichiometrically correlated) flow rate of oxygen as established bythe oxygen flow meter. The control system 120 is configured to limit thecontrol valves 148, 248 that, in turn, limit the output power of theburners 84.

The combustion system 100, and specifically the control system 120 canbe configured to meet any desired application for and in any industrythat relies on carbon based fuels. For example, in the present scrapaluminum processing plant 10, there are three applications or uses ofthe oxygen fueled combustion system 100. The first is for meltingaluminum in a high production environment (i.e., in the melting furnace14). Second, the system 100 is present in the holding furnace 16primarily for steady state temperature and alloy mixing of the moltenaluminum. The last application is in a dross-melting furnace 166 inwhich high temperature burners are used to release the metal units(aluminum which can be recovered for production) from the dross D (meltbyproduct) by thermal shock. In each use, the burners are installed forenergy conservation and environmental reasons.

Applications of the present combustion system 100 vary by thermal output(measured in maximum MMBTU per hour), size and orientation of theburners 84, as well as the temperatures at which the furnaces 14, 16,166 are designed to operate. Those skilled in the art will recognizethat mechanical differences (e.g., line sizes and the like) are neededto accommodate these differing needs, and that the specific programmingof the control system 120 and CPU 106 may vary.

The present combustion system 100 provides a number of advantages overknown and presently used combustion systems. For example, it has beenshown through operation that there is considerable energy savings usingthe present combustion system 100. The oxy-fuel burners 84 operate at amuch higher temperature than conventional furnaces. Thus, there is anobserved increase in the heat available for melt (in other industrialapplications, this increased heat can be made available for, forexample, steam generation, refuse incineration and the like). Thisprovides a reduction in the amount of fuel required to operate thefurnaces 14, 16, 166. In practice of the present invention, it has beenobserved that the average (and estimated) thermal input required perpound of aluminum melted is decreased from about 3620 BTU per pound (ina conventional furnace) to about 1083 BTU per pound in the meltingfurnace 14. This is a decrease of about 70 percent. In addition, thefuel needed to maintain temperature in the holding furnace 16 has beenshown to be about one-half of that of a conventional furnace.

It is believed that the fuel savings is attributed to three principalfactors. First, the increased heat of the combustion system 100 permitscomplete burn of all fuel without excess oxygen. Second, being held totheory, it is believed that the combustion system 100 operates within aradiative (or radiant) heat transfer zone, with some heat transfer byconduction.

The system 100 is designed to take advantage of the radiant heattransfer within the furnaces 14, 16, 166 to transfer heat effectively tothe metal baths. Third, because there is no nitrogen in the combustionprocess, the amount of gas flowing through the furnaces 14, 16, 166 islow. Thus, an increased residence time of the hot gases permits therelease of a larger proportion of energy (in the form of heat) prior toexhaust from the furnaces 14, 16, 166.

Typical exhaust gas volume is fractional of that of conventionalfurnaces. In that there is about 80 percent less gases (essentially thenitrogen component of air) in an oxy-fueled furnace, combustionefficiency is greatly increased. In conventional furnaces, the nitrogencomponent of air absorbs much of the energy (again, in the form of heat)from the melt. In the present combustion system 100, oxygen (rather thanair) and fuel are fed to the furnaces 14, 16, 166 and burned in astochiometric ratio. This is carried out without excess oxygen. Thus,there is no energy absorbed by non-combustion related materials e.g.,excess oxygen or nitrogen).

The present combustion system 100 also provides for increasedproduction. When installed as part of a melting furnace, the meltingcapacity or throughput of the furnace will be increased. This again isattributed to the rapid and effective heat transfer in the furnace 14.As new metal is introduced into the furnace 14, the combustion system100 responds rapidly to provide heat to melt the fed metal and tomaintain the heat (temperature) of the molten metal in the pool 60 atthe set point temperature. It has been found that aluminum accepts heatvery efficiently from a radiative heat source.

Perhaps most importantly, is the reduced environmental impact of thepresent combustion system 100, compared to presently known and usedcombustion systems. The present system 100 advantageously uses nonitrogen (from air) in the combustion process. Typically, NOx productionoccurs in a furnace as a reaction product of the heated air that is fedby the combustion system. However, in that the present system 100 usesoxygen, rather than air, any NOx produced by the present combustionsystem is due solely to the amount of elemental nitrogen that is in thefuel (i.e., fuel-borne nitrogen). In that fuel-borne nitrogen levels areextremely low (compared to that contributed by air in conventionalfurnaces), the NOx levels of the present combustion system are wellbelow any industry standards and governmental limitations. In additionto reducing NOx production, the production of other green-house gases,such as carbon monoxide, is also greatly reduced.

In addition, to the reduced environmental impact, the present oxy fuelcombustion system conserves energy because significantly more aluminumcan be processed at considerably less fuel input (any carbon based fuel,including coal, coal dust, natural gas or oil). As a result ofprocessing with less fuel usage, conservation of fuel resources isachieved. Essentially, less fuel is used in the aggregate, as well as ona per pound basis to produce aluminum. This reduces processing (e.g.,fuel) costs, as well as the taxing use of fossil fuels.

Oxygen Supply

As will be recognized by those skilled in the art, the oxygenrequirements for the present combustion system 100 can be quite high. Tothis end, although oxygen can be purchased and delivered, and stored foruse in the system, it is more desirable to have an oxygen productionfacility near or as part of an oxy fuel combustion system, such as theexemplary scrap aluminum processing plant.

Referring now to FIG. 4, there is shown a cryogenic plant 180 for usewith the present combustion system 100. The illustrated, exemplarycryogenic plant 180 produces 105 tons per day of at least 95 percentpurity oxygen and 60,000 standard cubic feet per hour of nitrogen havingless then 0.1 part per million oxygen. The plant 180 includes a 1850horsepower three-stage compressor 182. The compressed air, at 71 psigenters a purifier/expander 184. The air exits the expander 184 at apressure of 6.9 psig and a temperature of −264° F., and enters acryogenic distillation column 186. In the column 186, air is separated(distilled) into gaseous nitrogen, liquid nitrogen, gaseous oxygen andliquid oxygen. The gaseous oxygen, indicated generally at 188, is feddirectly to the combustion system 100 and the liquid oxygen, indicatedgenerally at 190, is stored for example in tanks 191, for later use forin the combustion system 100. The oxygen pressure from the cryogenicplant 180 may be lower than that required for the combustion system 100.As such, an oxygen blower 192 is positioned between the oxygen dischargefrom the column 186 and the combustion system 100 feed to raise thepressure to that need for the combustion system 100.

The gaseous nitrogen, indicated generally at 194, is fed to a downstreamannealing/stress relieving system (not shown) within the plant 10. Thesesystems, which use nitrogen to treat aluminum to relieve stresses in themetal and to anneal the metal, will be recognized by those skilled inthe art. In addition, the nitrogen 194 is used in the degassing units24. The plant 10 also includes a back up supply of oxygen and nitrogen191, 196, respectively, in liquid form in the event of, for example,maintenance or other situations in which the cryogenic plant 180 cannotsupply the plant requirements. The back-up systems 191, 196 areconfigured to automatically supply oxygen and/or nitrogen as required,such as when the cryogenic plant 180 is off-line. Excess nitrogen can bestored, bottled and sold. Systems such as these are commerciallyavailable from various manufacturers, such as Praxair, Inc. of Danbury,Conn.

Heat Recovery

The aluminum processing system 10 also takes advantage of waste heatfrom the various processes. Specifically, the processing plant 10 caninclude a waste heat recovery system, indicated generally at 200 in FIG.4. Exhaust gas, indicated at 202, from the melting furnace 14 and theholding furnace 16 is directed to one side of a waste heat recovery heatexchanger 204. In that the exhaust gas 202 is at a temperature of about1000° F., there is a considerable amount of energy that can berecovered. In addition, energy can be recovered from the exhaust abovethe main furnace bath area 60.

The exhaust gas 202 is directed to the waste heat exchanger 204. Aworking fluid, indicated at 206, such as pentane, flows through theother side of the heat exchanger 204 under pressure. It is anticipatedthat a plate-type heat exchanger or a plate-and-tube type heat exchangeris best suited for this application. Those skilled in the art willrecognize the various types of working fluids that can be used for thepresent waste heat recovery system, as well as the heat exchange systemsthat are used with these types of working fluids. All such systems arewithin the scope and spirit of the present invention.

The heated fluid 206 is then directed to a vaporizer 208 where the fluid206 is allowed to expand into vapor. The vapor 206 is directed to aturbine-generator set 210 to produce electricity. The vapor is thencondensed, in a condenser 212, and returned to the heat exchanger 204.It is anticipated that sufficient energy to produce about 1.5 to 2.0megawatts of power in the form of electricity can be recovered from theexhaust gas 202 from the above-described scrap processing plant 10.

Although a wide variety of working fluids 206 can be employed for use insuch a waste heat or waster energy recovery system 200, in a presentlycontemplated system, pentane is used as the working fluid 206. Such anorganic based system provides a number of advantages over, for example,steam-based systems. It is anticipated that a pentane-based workingfluid 206, in a standard Rankine-cycle arrangement will allow forvariations in vapor supply more readily than a steam-based system. Inthat the heat output from the furnaces (melting 14 and holding 16) isdependent upon metal production, rather than electrical needs, theenergy input to the recovery system 200 is likely to vary and will bethe controlling characteristic for power production. As such, a fluid206 such as pentane provides the greater flexibility that is requiredfor such a recovery system 200.

As will be recognized by those skilled in the art, the electrical powergenerated can be used to provide some of the power necessary for thescrap processing plant 10, including the cryogenic plant 180. Power foroperating the plant 10 can be provided by an oxy fueled combustionsystem employed in an electric power generating plant (using a furnaceor boiler), to generate steam for a steam turbine-generator set. In suchan arrangement, when the power generated exceeds plant 10 requirements,the excess power can be sold to, for example, a local electric utility.

Dross Processing

Referring now to FIG. 2, the contaminants or dross D from the meltingfurnace 14 is further processed, separate and apart from the in-linealuminum recovery in a dross recovery process, indicated generally at164. The dross D is removed, as by skimming, from the top of the moltenaluminum pool 60 in the melting furnace 14. The dross D is pressed in asieve-like bowl 168 by mechanical means. Pressing pushes the aluminum Afrom the dross D, through openings 170 in the bowl 168. The aluminum Athat is pressed from the dross D is recovered and is returned to themelting furnace 14.

The oxide laden dross is fed into the recovery furnace 166 forreheating. The recovery furnace 166 is of a similar design to themelting furnace 14 in that it uses an oxy-fuel combustion system 100design. In operation, however, the recovery furnace 166 “shocks” thedross laden material by using near direct flame impingement of about5000° F. to release the aluminum metal from the dross D. The molten bath172 temperature in the recovery furnace 166 is also considerably higher,about 1450° F.-5000° F., with a furnace air temperature of about 2000°F.-2200° F. In addition, the “shocking” process is carried out in ahighly reduced atmosphere with substantially no excess oxygen within thefurnace 166 (in contrast to conventional furnaces that operate at excessoxygen levels of about 3 to 5 percent).

The recovery furnace 166 is likewise skimmed and the resulting dross ispressed. The recovered aluminum A is transferred to the melting furnace14. The remaining dross D2 is then sent for processing off-site, to adross processor, for further aluminum recovery. It has been found thatthe present process, including the dross recovery process, provides asignificant increase in the recovery of metal. The dross D2 that isultimately shipped for further processing is only a fraction of theoriginal quantity of dross D, thus reducing processing costs andincreasing aluminum recovery.

Importantly, the present dross recovery process 164 is carried outwithout the use of salts or any other additives. Rather, thermalshocking is used to release the metal from the oxides. Known recoveryprocesses use salts to separate the oxides from the metal. In that thesalts remain in the oxides, which are in turn disposed of, ultimately,the salts are likewise sent for disposal. These salts can beenvironmental hazards and/or toxic. As such, the present process 164 isenvironmentally beneficial in that it eliminates the need for thesesalts and thus their disposal.

As to the overall processing scheme 164, again, it has been found thatthe present recovery steps (e.g., double pressing with intermediatereheating) result in aluminum recovery rates that are significantlyimproved over those of known processes, depending upon the grade of thescrap. Multi-percent increases in the amount of metal recovered from thedross D have been achieved.

Other Applications for the Combustion System

As discussed above, it is apparent that increased efficiencies from theuse of oxygen in all continuous processes can be achieved. For example,power generating plants can increase flame temperature or reduce LOI inboilers by introducing oxygen to the burning formula (rather than air).This can increase efficiencies in operation. Essentially, burning of anycarbon based fuels can be enhanced by the introduction of oxygen. Thebenefits are both economical and environmental. To date no industryother than glass-making has embraced oxy fuel technology. In the glassmaking industry this technology is used not for the efficiencies thatresult, but because of the high melting temperature required for theglass production process.

Nevertheless, use of oxy-fueled combustion systems in all industrial andpower generating applications can provide reduced fuel consumption withequivalent power output or heat generation. Reduced fuel consumption,along with efficient use of the fuel (i.e., efficient combustion)provides greatly reduced, and substantially zero, NOx emissions andsignificant reductions in the emission of other green-house gases.

Due to the variety of industrial fuels that can be used, such as coal,natural gas, various oils (heating and waste oil), wood and otherrecycled wastes, along with the various methods, current and proposed,to generate oxygen, those skilled in the art will recognize the enormouspotential, vis-a-vis industrial applicability, of the present combustionsystem. Fuel selection can be made based upon availability, economicfactors and environmental concerns. Thus, no one fuel is specified;rather a myriad, and in fact, all carbon based fuels are compatible withthe present system. In addition, there are many acceptable technologiesfor producing oxygen at high purity levels. Such technologies includescryogenics, membrane systems, absorption units, hydrolysis and the like.All such fuel uses and oxygen supplies are within the scope of thepresent invention. Those skilled in the art will recognize that theother gases produced, such as hydrogen and nitrogen, can be stored,bottled and sold.

As discussed in detail above, one application for the present combustionis scrap aluminum processing or recovery. Other exemplary applications,as will be discussed below, include industrial power generation boilersand incinerators. These exemplary applications focus on the flexibilityand applicability of this technology for broad industrial uses.

In general, the use of oxygen fuel fired combustion over current ortraditional air fuel systems offers significant advantages in manyareas. First is the ability to run at precise stoichiometric levelswithout the hindrance of nitrogen in the combustion envelope. Thisallows for greater efficiency of the fuel usage, while greatly reducingthe NOx levels in the burn application. Significantly, less fuel isrequired to achieve the same levels of energy output, which in turn,reduces the overall operating costs. In using less fuel to render thesame power output, a natural reduction in emissions results. Fuelsavings and less emissions are but only two of the benefits provided bythe present system.

Steam generators for the production of electricity, e.g., by industrialpower boilers, are varied but are nevertheless fundamentally dependentupon their combustion systems to produce steam to turn aturbine-generator set. The fuels used vary based upon the design of thesteam generators. However, all of the boilers require an oxidizingagent. Using the present oxy fuel combustion system, high purity oxygenis used as the sole oxidizing agent throughout the boiler or is used asa supplement to air providing the oxygen for combustion.

The benefits that can be enjoyed by other industrial applications holdtrue for the power industry. For example, the use of oxygen within thecombustion zone enhances flame temperature while effectively cutting LOI(loss on ignition) by providing readily available oxygen for combustion.By increasing flame temperatures, greater rates of steam generation canbe accomplished with the same fuel burn rate. Conversely, equal powergeneration or output can be recognized with lower fuel burn rates. Flametemperature will be dependent upon the concentration of the oxygenprovided for combustion. To this end, with no oxygen supplementation orenrichment (i.e., pure air for combustion), flame temperatures will beabout 3000° F. Referring to the above discussion, with pure oxygen asthe oxidizing agent, the flame temperature will be about 4500° F. toabout 5000° F. The anticipated flame temperatures for varying degrees ofoxygen supplementation can be interpolated (it is believed linearly)between these temperatures.

Oxygen can also be used in conjunction with over-fired air systems orlox NOx burners to reduce NOx and other green-house gases while ensuringstable flame at stoichiometry. Typical low NOx burners often increaseLOI. This requires operators to burn more fuel. By adding enrichedoxygen to the combustion process complete burn becomes available forfuel while at stoichiometry without additional nitrogen present (byadditional air input) to create NOx.

It is anticipated that boilers will be designed around oxygen fueledcombustion systems to take full advantage of the benefits of thesesystems. It is also anticipated that retrofits or modifications toexisting equipment will also provide many of these benefits both to theoperator (e.g., utility) and to the environment.

For example, FIG. 12 illustrates, schematically, a coal fired boiler orfurnace 300. A wind box 302 is formed at a wall 304 of the furnace 300.A burner 306, through which the coal is introduced into the furnace 300,extends through the wind box 302. The coal is carried to the furnace 300by a coal conduit 308. Primary air (as indicated at 310) is supplied tocarry the coal (from a pulverizer, not shown) through the conduit 308and burner 306 into the furnace 300. Tertiary air (as indicated at 312)is provided to the coal conduit 308 to assure that the coal is conveyedto the burner 306.

Secondary air (as indicated at 314) is provided from the wind box 302directly into the furnace 300 through registers 316 on the furnace wall304. The secondary 314 air is the primary source of air for thecombustion process. In one well recognized and known system forcontrolling NOx, an over-fired air system (as indicated at 318) injectsair (from the wind box 302), into the furnace 300 over the flame F. Theunderlying purposes for the over-fired air are two-fold. First is toprovide sufficient oxygen to assure complete combustion of the fuel.Second is to reduce the flame temperature and thereby reduce theproduction of NOx.

It is anticipated that the present combustion system can replaceexisting combustion systems, in total, or, in the alternative, can beused to provide an oxygen supplement to the air used for combustion.Specifically, it is anticipated that high purity oxygen can be used inplace of any or all of the primary 310, secondary 314 and tertiary air312 that is used in these known combustion systems. Those skilled in theart will recognize the benefits that can be obtained using the presentoxy fuel combustion system (or as in certain applications oxygensupplementation system) in power boilers or furnaces that use otherfossil fuels, such as oil or gas.

Use of the present combustion system is also contemplated for use inconnection with industrial waste incinerators. Typical wasteincinerators operate on the basis of resonant time, temperature andexcess oxygen. An oxy-fuel system will allow for greater efficiency inthe operation.

Resonant time is dependent upon the physical size of the heated chamberor stack, and the velocity and volume of gases passing through thechamber or stack. As nitrogen is taken out of the mix the resonant timenaturally increases because the volume of gas used in the combustionprocess is less (by about 80 percent). When an incinerator isspecifically designed with an oxy-fuel combustion system, theincinerator requires considerably less capital cost because of thereduced size that is required.

Typical flame temperatures of oxy-fueled combustion systems are muchhigher then air fueled systems. Thus, the efficiency of the burnultimately requires less thermal input from the fuel, resulting in lessoperating costs. One of the benefits of the oxy-fuel combustion systemis the control over excess oxygen levels that is achieved. In the caseof conventional incinerators, excess oxygen is required to burn thevolatile organic carbons (VOCs) and unburned carbon. This excess oxygenis provided by injecting air into the chamber or stack where the oxygen(from the air) is used to complete the burn of VOCs and unburned carbon.Although air provides the necessary excess oxygen, it also permitsnitrogen into the chamber. The excess nitrogen that is introduced (toprovide the excess oxygen) results in increased production of NOx.Additionally, the excess air, overall, results in the generation ofother green-house gases, and further acts to cool the chamber. Thisundesirable cooling then requires additional heat from the combustionsystem to overcome this cooling effect.

FIG. 13 illustrates, schematically, a typical industrial furnace 400.Waste (as indicated at 402) is introduced into a stack 404. A burner 406is fed with air (as indicated at 408) and fuel (as indicated at 410) toproduce a flame F to incinerate the waste 402. A carbon monoxide (CO)monitor 412 is located above the flame F to determine the level of CO inthe exhaust gas. When the level of CO is too high, additional air is fedto the burner 406. Optionally, air can be fed into the stack from alocation 414 apart from the burner 406 to provide the additional air.

There are a number of drawbacks to this method of operation. Asdiscussed above, the two controlling factors in waste incineration aretime and temperature. That is, higher temperatures and greater resonanttimes increase the incineration of the waste. However, the addition ofair (to reduce CO levels) increases the flow rate through the stack 404thus reducing the resonant time. In addition, although the increased airflow reduces flame temperatures (which in turn reduces NOx production),it also introduces high levels of nitrogen, which tends to increase NOxproduction and offset the cooling (and reduced NOx production) effect.Moreover, because of the cooling effect of the air, the efficiency ofthe incineration process is reduced.

The present oxy-fuel combustion system, on the other hand, uses highpurity oxygen which permits burning the unburned material without theproduction of NOx and other green-house gases and without coolingeffects. The present oxy-fuel system thus affords several advantagesover conventional or traditional incinerator systems. In that theprimary duty of an incinerator is to burn VOCs and other contaminantsbefore they reach the atmosphere, the present combustion system reducesthe fuel used and thus results in reduced production of NOx and othergreen-house gases, and a reduced volume of flue gases generally.

In addition, the installation (e.g., capital) and operating costs ofincinerators employing oxygen fueled combustion systems will be greatlyreduced. The capital cost of the incinerator will be reduced because thevolume of gases through the system is expected to be much lower. Asprovided above, because the throughput of gas is much less, the overallsize of the incinerator can be considerably less than conventionalsystems while maintaining the same resonant time. Thus, the incineratorcan be physically smaller to handle the same waste load, and therequired support systems and ancillary equipment and systems canlikewise be smaller.

In addition, oxy-fueled combustion systems are generally considerablymore efficient than conventional incinerator systems and require afractional amount of the required energy input. The system also lendsitself quite well to incinerator applications in which the fuel isunburned carbon or VOCs. Likewise since there is no nitrogen present inthe flame envelope the development of NOx is kept to a minimum,relegated to NOx formed from fuel-borne nitrogen only.

The industries described above are only a few exemplary industries thatcan benefit from the use of the present oxy fuel combustion system.Those skilled in the art will recognize the applicability of this systemin the chemical and petro-chemical industries, the power generationindustry, plastics industries, the transportation industry and the like.

Oxy Fuel Combustion—The Benefits and Advantages

The benefits and advantages of oxy fuel combustion will be appreciatedby those skilled in the art. Nevertheless, in an exemplary aluminumscrap processing facility, using an air-fired furnace outfitted fornatural gas, it was found that the energy required to process or meltone pound of scrap aluminum (as determined by the cubic feet of naturalgas used), was 3,620 BTUs (presented as 3,620 BTUs/lb). That is, about3.45 standard cubic feet (SCF) of natural gas was need to melt eachpound of aluminum. The energy requirement of 3,620 BTU is based uponeach SCF of natural gas having a heat content of 1,050 BTUs.

In contrast, using the present oxy fueled combustion system, it wasfound that only 1.03 SCF of natural gas (or 1083 BTUs) was needed tomelt each pound of aluminum. Thus, the present oxy fuel combustionsystem used 1083BTU/3620BTU or 29.9 percent of the fuel required for anair-fired furnace. This is a reduction of 1.0 less 0.299 or about 70percent in the fuel consumption.

Similar though not quite as drastic reductions in fuel consumption havebeen observed with an oxy fueled combustion system that uses waste oilas a fuel. It was found that the heat content of the waste oil fuel needto melt each pound of aluminum was 1218 BTUs. Thus, the reductionobserved with waste oil was {fraction (1218/3620)} or 33.6 percent,resulting in a reduction in fuel consumed of about 66 percent. As such,even before considering the reduction in pollutants produced, thepresent oxy fuel combustion system exhibited reductions in fuelconsumption of about 70 percent and 66 percent using natural gas andwaste oil, respectively, over an air-fired, natural gas fired furnace.

Table 1, below illustrates a comparison of the pollutants produced usingan air-fired (gas fueled, shown as “AIR-GAS”) combustion system, an oxyfueled (gas, shown as “OXY-GAS”) combustion system and an oxyfueled-(waste oil, shown as “OXY-OIL”) combustion system. The pollutantsshown are carbon monoxide (CO), gaseous nitrogen compounds (NOx),particulate matter under 10 microns in size (PM10), total particulatematter (PT), sulfur containing gaseous compounds (SOx) and volatileorganic carbon compounds (VOC).

The data is shown in two forms, namely, tons per year produced (TPY) andpounds produced per million BTUs used (lbs/MMBTU). The parentheticalsfollowing the OXY-GAS and OXY-OIL data represent pollutant reductionsover those of the air-fired, gas fueled combustion system.

TABLE 1 FLUE GAS ANALYSIS FOR AIR-GAS, OXY-GAS AND OXY-OIL COMBUSTIONSYSTEMS AIR-GAS OXY-GAS OXY-OIL Pollutant TPY lb/MMBTU TPY lb/MMBTU TPYlb/MMBTU CO 4.88 2.0E−2 1.51 6.0E−3 1.32 5.0E−3 (68.9) (73.0) NOx 24.381.E−1 0 0 (100.0) 10.04 0.041 (58.8) PM10 .028 1.0E−4 .0023 9.4E−6 (92)0.146 6.0E−4 (−410) PT .028 1.0E−4 .0023 9.4E−6 (92) 0.169 6.9E−4 (−490)SOx 0.146 6.0E−4 4.5E−2 1.9E−4 (69) 1.39 5.7E−3 (−848) VOC 0.582 2.4E−34.0E−1 1.6E−3 (31) 3.33 1.4E−2 (−471)

The values for PM10, PT, SOx and VOC for the oxy fueled waste oilcombustion system show increases (as negative reductions). This is duein part to no “post-burn” treatment processes used in the exemplarycombustion system. It is anticipated that proper “post-burn” processeswould include bag houses (for particulate matter) and scrubbers (forsulfur-containing gases) and would result in reductions of at leastabout 98.99 percent and 95 percent, respectively, in emissionsquantities. The values attained in TABLE 1 were based upon the reductionin fuel consumption observed and were determined in accordance withaccepted United States Environmental Protection Agency (USEPA) criteria,as determined from USEPA tables AP42 (available from the USEPA website).

It must be noted that the above values are based upon controlling theenvironment within the furnace in which the oxy fueled combustion systemis used. That is, the values shown above that indicate reductions inpollutants for the OXY-GAS and OXY-OIL combustion systems require thatthe furnace in which the combustion systems are installed is designed tolimit to negligible air in-leakage (i.e., nitrogen in the combustionatmosphere).

Thus, as will be appreciated by those skilled in the art, the use ofhigh purity oxygen (or highly oxygen-enriched air) and any carbon basedfuel is highly adaptive to many existing industrial systems. It isanticipated that the uses for such a system in standard and conventionalindustrial applications will provide myriad advantages and benefits overknown, presently used air fired and air over-fired systems. Althoughmany present physical plants may require redesign and modification toincorporate the present oxy-fueled combustion systems to enhanceperformance and production, it is contemplated that the benefits gainedby making these changes in design and structure, such as loweredoperating costs, e.g., reduced fuel costs, lowered capital costs andreduced emissions, will far outweigh the costs to make these changes.

In the present disclosure, the words “a” or “an” are to be taken toinclude both the singular and the plural. Conversely, any reference toplural items shall, where appropriate, include the singular.

From the foregoing it will be observed that numerous modifications andvariations can be effectuated without departing from the true spirit andscope of the novel concepts of the present invention. It is to beunderstood that no limitation with respect to the specific embodimentsillustrated is intended or should be inferred. The disclosure isintended to cover by the appended claims all such modifications as fallwithin the scope of the claims.

What is claimed is:
 1. A method for recovering aluminum from aluminummixed with other than aluminum materials including the steps of: feedingaluminum mixed with other than aluminum materials into a meltingfurnace, the furnace configured to substantially prevent theintroduction of air; feeding oxygen at a predetermined purity greaterthan 21 percent into the furnace; feeding a carbon based fuel into thefurnace; combusting the oxygen and the carbon based fuel in the furnace,the oxygen and carbon based fuel combusted in the furnace wherein theoxygen in the oxygen supply and the carbon based fuel are fed into thefurnace in a stoichiometric proportion to one another to limit an excessof either the oxygen or the carbon based fuel to less than 5 percentover the stoichiometric proportion, and wherein the combustion of thecarbon based fuel provides a flame temperature in excess of about 4500°F., and wherein an exhaust gas stream from the furnace has a temperatureof not more than about 1100° F.; melting the aluminum in the furnace;removing contaminant laden aluminum from the furnace; and dischargingsubstantially pure molten aluminum from the furnace.
 2. The method forrecovering aluminum in accordance with claim 1 including to step ofrecovering waste heat from the furnace.
 3. The method for recoveringaluminum in accordance with claim 1 including the step of recoveringaluminum from the contaminant laden aluminum laden and charging therecovered aluminum into the furnace.
 4. The method for recoveringaluminum in accordance with claim 2 including the step of converting thewaste heat to electricity.
 5. A salt-less method for separating aluminumfrom dross-laden aluminum comprising the steps of: introducing thedross-laden aluminum into a furnace, the furnace configured tosubstantially prevent the introduction of air, the furnace having anoxygen fuel combustion system for combustion of a carbon-based fuel withoxygen at a predetermined purity greater than 21 percent to produce aflame temperature of about 5000° F., and having substantially no excessoxygen, the dross-laden aluminum melting within the furnace; skimming anupper portion of the melted dross-laden aluminum to produced a heavilydross-laden product; pressing the heavily dross-laden product in amechanical press to separate the aluminum from the heavily dross-ladenproduct to produce a concentrated heavily dross-laden product.
 6. Thesalt-less method for separating aluminum from dross-laden aluminum inaccordance with claim 5 including the step of returning the concentratedheavily dross-laden product to the furnace.
 7. The salt-less method forseparating aluminum from dross-laden aluminum in accordance with claim 5including near direct flame impingement introduction of the dross-ladenaluminum into the furnace.
 8. The method for recovering minimum inaccordance with claim 1 including the stop of feeding the carbon basedfuel into the melting furnace at a rate that is dependent upon a feedrate of the oxygen.
 9. The method for recovering aluminum in accordancewith claim 1 including the step of feeding the oxygen into the meltinginciting furnace at a rate that is dependent upon a feed rate of thecarbon based fuel.
 10. The method for recovering aluminum in accordancewith claim 1 including the step of controlling at lest one of thefeeding the carbon-based fuel and feeding the oxygen so as to maintainone or more temperatures in the furnace at or below one or more desiredtemperatures.
 11. The method for recovering aluminum in accordance withclaim 10 wherein the one or more desired temperatures are based, inpart, upon the heat transfer as affected by a geometry of the meltingfurnace.
 12. The salt-less method for separating aluminum in accordancewith claim 5 including the step of supplying the carbon based fuel intothe furnace at a rate that is dependent upon a feed rare of the oxygen.13. The salt-less method for separating aluminum in accordance withclaim 5 including the step of feeding oxygen into the furnace at a ratethat is dependent upon a feed rate of the carbon based fuel.
 14. Thesalt-less method for separating aluminum in accordance with claim 5including the step of controlling at least one of a carbon-based fuelsupply and an oxygen supply so as to maintain one or more temperaturesin the furnace at or below one or more desired temperatures.
 15. Thesalt-less method for separating aluminum in accordance with claim 14wherein the one or more desired temperatures are based, in part, uponthe heat transfer as affected by a geometry of the furnace.